An X-ray CT apparatus irradiates an X-ray of a fan beam or cone beam (conical shape or pyramid shape) to an object to be examined, acquires projection data which is the information related to intensity of the X-ray that is transmitted through the object, and scans distribution information of X-ray absorption coefficient in the object based on the acquired projection data.
The X-ray CT apparatus acquires projection data in discrete X-ray tube positions (views). The view number per one rotation of an X-ray tube normally reaches from several hundreds to several thousands. The X-ray CT apparatus executes scanning by irradiating an X-ray while rotating an X-ray tube around the object, and acquires projection data of the view number necessary for reconstructing a piece of tomographic image (CT image).
As for the scan condition of an X-ray CT apparatus, when an X-ray tube current is constant, there are cases that radiation dosage is excessive or insufficient depending on the irradiation angle of an X-ray or an irradiation target region. In response, the technique for an X-ray CT apparatus has been proposed which is to achieve suppression of radiation dose and improvement of image quality by controlling an X-ray tube current by measuring X-ray transmission data of the object during scan in real time (for example, refer to [Patent Document 1]).
Also, a technique for an X-ray CT apparatus has been proposed which is to calculate an elliptic cross-section model of the object from scanogram projection data, and calculate an X-ray tube current value using the area and the aspect ratio of the elliptic cross-section (for example, refer to [Patent Document 2]).
Also, a technique for an X-ray CT apparatus has been proposed which is to modify an object cross-sectional model considering the weight of the object or information on injection amount and density of contrast agent in an examination using contrast agent (for example, refer to [Patent Document 3]).
Patent Document 1: JP-A-H10-309271
Patent Document 2: JP-A-2001-043993
Patent Document 3: JP-A-2005-305026